1. Field of the Invention
The present invention relates to a nuclear reactor in which heat generated by nuclear fission in the reactor core is used, and particularly to a nuclear reactor of an indirect cycle type in which heat of the primary system of the nuclear reactor is used outside the pressure vessel using a heat exchanger.
2. Prior Art
An example of a system for removing decay heat generated in the reactor core during reactor shutdown is a residual heat removal system described, for example, in xe2x80x9cA Textbook of Nuclear Power Generation Technology (Ohm Publication Co.)xe2x80x9d PP. 172. This is a system for removing decay heat after lowering temperature of the primary system using the main condenser, and performs heat removal by a heat exchanger outside the containment vessel using the reactor water recirculation pump. Further, a reactor core isolation cooling system is provided in order to cope with a case of occurrence of a failure in the main condenser or the like. Steam generated by the decay heat in the reactor core is released to the pressure suppression pool through a relief valve, and a pump driven by a steam turbine makes up for lowering of water surface level in the pressure vessel by supplying water in a condensate storage tank into the pressure vessel.
As a second example, in regard to the system removing decay heat generated in the reactor core during reactor shutdown in the nuclear reactor in which heat of the primary system of the nuclear reactor is used outside the pressure vessel using a heat exchanger, a decay heat removal system is disclosed, for example, in Japanese Patent Application Laid-Open No.1-172800.
The system is that decay heat is heat-exchanged by a secondary system heat exchanger inside the pressure vessel, and the decay heat removed by conducting generated steam to heat pipes arranged in pool water outside the containment vessel to be condensed.
On the other hand, as a third example, in regard to the nuclear reactor in which heat of the nuclear reactor primary system generated in the reactor core is used outside the pressure vessel using a heat exchanger, a natural circulation nuclear reactor is disclosed, for example, in Japanese Patent Application Laid-Open No.58-156888. The nuclear reactor is a system that heat exchangers are arranged above the water surface level and below the water surface level inside the pressure vessel, and the heat exchanger above the water surface level conducts heat to the secondary cooling water mainly by condensation of the primary cooling water vapor, and the heat exchanger below the water surface level conducts heat to the secondary cooling water by convection heat transfer of the primary cooling water.
The heat exchanger below the water surface level is also used for controlling a subcooling degree of the primary cooling water flowing into the reactor core. The secondary cooling water lowing into and out of the heat exchanger communicates with the outside of the pressure vessel through a flow passage penetrating through the side wall surface of the pressure vessel.
As a fourth example, a natural circulation nuclear reactor is disclosed in Japanese Patent Application Laid-Open No.60-135890. The nuclear reactor is a system that a cylindrical baffle having a cross section wider then a shroud is arranged in an upper portion of the shroud to prevent the water surface level from swilling up due to jet flow and to prevent condensing heat transfer of a heat exchanger from being lowered by direct contact of the cooling water to the heat exchanger.
As a fifth example, a heat supplying nuclear reactor is disclosed in Patent Application Laid-Open No.2000-221291. The nuclear reactor is a system that a plate-shaped baffle plate is arranged in a portion of the shroud to prevent condensing heat transfer of a heat exchanger from being lowered by direct contact of the cooling water to the heat exchanger.
In the example of the system described in xe2x80x9cA Textbook of Nuclear Power Generation Technologyxe2x80x9d, the first edition, the fourth print, page 172 to page 173, published on May 20, 1972 by Ohm Publication Co., there is a problem in that the economic feasibility in relation to construction of the nuclear reactor is decreased because the system composed of active components for removing decay heat needs to be routed to the outside of the containment vessel.
Further, in the indirect cycle nuclear reactor, a system for cooling the primary system and for preventing the primary system cooling water from flowing out to the inside of the containment vessel is important when the main condenser can not be used. In the example shown in the Japanese Patent Application Laid-Open No.1-172800, there is a problem in that the economic feasibility in relation to construction of the nuclear reactor is decreased because the system for removing decay heat needs to be routed to the outside of the containment vessel.
Further, in the example shown in Japanese Patent Application Laid-Open No.58-156888, because opening portions such as nozzles are arranged at portions below the water surface level in the pressure vessel, there is a possibility that the primary cooling water may flow out in an event of occurrence of a rupture in the opening portion though it hardly occurs.
Therefore, it is necessary to provide a safety system in considering the event that the primary cooling water may flow out. Further, when the heat exchanger is taken off at maintenance of the pressure vessel, it is required that the heat exchanger is taken off from the pressure vessel wall after removing the upper vessel head of the pressure vessel, and then the heat exchanger is pulled upward.
In the examples shown in Japanese Patent Application Laid-Open No.60-135890 and Patent Application Laid-Open No.2000-221291, the heat transfer area of the heat exchange is limited because the plenum portion in the outer side of the baffle plate where the heat exchanger is contained is narrow. Therefore, it is necessary to make the heat exchanger tall on order to secure a designed output power. Accordingly, there is a problem in that the economic feasibility in relation to construction of the nuclear reactor is decreased because a height of the pressure vessel and a height of the containment vessel become higher.
A first object of the present invention is to provide a highly safe nuclear reactor in which the primary system cooling water never leaks to the outside of the containment vessel at occurrence of such a failure that the main condenser can not be used, or at occurrence of a failure or a rupture in the heat exchanger.
A second object of the present invention is to provide a highly safe nuclear reactor which has a low possibility of leaking the primary system cooling water, and the highly safe nuclear reactor is also easy in manipulability at maintenance of the pressure vessel.
A third object of the present invention is to provide a highly economical nuclear reactor of which the reactor pressure vessel and the containment vessel are small in size.
A fourth object of the present invention is to provide a highly economical nuclear reactor of which the thermal output of the nuclear core is high, and the highly economical nuclear reactor is also high in operability.
A fifth object of the present invention is to provide a highly economical nuclear reactor of which the thermal output of the nuclear core is further increased.
The first object described above can be attained by a nuclear reactor comprising a heat exchanger arranged in a pressure vessel, the heat exchanger being heated by primary cooling water heated by a reactor core to generate steam to be supplied to a turbine or a heat supply system; and a heat exchanger arranged under water of a pressure suppression pool in a containment vessel, wherein a secondary steam flow passage of the heat exchanger inside the pressure vessel is branched, the branched pipe communicating with the heat exchanger inside the pressure suppression pool through an isolation valve; a secondary cooling water flow passage of the eat exchanger inside the pressure vessel being branched, the branched pipe communicating with the heat exchanger inside the pressure suppression pool through an isolation valve; decay heat generated in the reactor core during reactor core isolation being heat exchanged by the heat exchanger inside the pressure vessel, steam generated by the decay heat being condensed by the heat exchanger inside the pressure suppression pool, at the same time the condensed water being supplied to the heat exchanger inside the pressure vessel.
The second object described above can be attained by a nuclear reactor comprising a heat exchanger arranged in a pressure vessel, the heat exchanger being heated by primary cooling water heated by a reactor core to generate steam to be supplied to a turbine or a heat supply system, flow passages of secondary steam generated in the heat exchanger and secondary cooling water supplied to the heat exchanger being inserted from the head portion of the pressure vessel, at the same time the heat exchanger being placed at a level above the water surface level inside the pressure vessel, steam of the primary cooling water being condensed to transfer the heat to the secondary cooling water in the heat exchanger, the heat exchanger being supported together with control rod drive shafts by the head of the pressure vessel.
The third object described above can be attained by a nuclear reactor comprising an annular baffle plate arranged above a shroud, the annular baffle plate having a flow passage cross-sectional area smaller than that of the shroud; a heat exchanger arranged outside the baffle plate inside the pressure vessel; and a gap formed between an upper portion of the shroud and the baffle plate. Further, the third object described above can be attained by a nuclear reactor, wherein one or more baffle plates are arranged inside the baffle plate so as to intersect at right angle with flow direction of two-phase cooling water flowing from the inside of the shroud into the baffle plate, and a plurality of flow-passage holes are formed in the baffle plates intersecting at right angle with the flow direction of two-phase cooling water. Furthermore, the third object described above can be attained by a nuclear reactor, wherein in a case of arranging a plurality of the baffle plates intersecting at right angle with the flow direction of two-phase cooling water, the plurality of flow-passage holes on the baffle plates intersecting at right angle with the flow direction of two-phase cooling water are formed by varying positions for each of the baffle plates intersecting at right angle so as to improve stem separation effect by varying direction of the two-phase cooling water flowing into the baffle plate from the inside of the shroud between the baffle plates intersecting at right angle with the flow direction of two-phase cooling water.
The fourth object described above can be attained by a nuclear reactor comprising a heat exchanger or a superheater arranged inside the baffle plate in the pressure vessel, the heat exchanger being heated by primary cooling water heated in the reactor core and generating steam, the superheater superheating the steam of secondary cooling water generated in the heat exchanger, the generated steam of the superheated steam being supplied to a turbine or a heat supply system; and a preheater for the secondary cooling water arranged inside the downcomer.
The fifth object described above can be attained by a nuclear reactor comprising the plurality of the baffle plates intersecting at right angle with the flow direction of two-phase cooling water, flow-passage holes being formed on each of the baffle plates intersecting at right angle with the flow direction of two-phase cooling water, the plurality of flow-passage holes being formed so as to vary positions for each of the baffle plates intersecting at right angle.